How to flush stdin buffer before calling `read_key()`?

I'd like to be able to prevent keypresses from being recognized before read_key() is actually called. Currently I'm doing the following:

let term = Term::stdout();

thread::sleep(Duration::from_secs(5));

match term.read_key()? {
    _ => ...
}

I'd like for any keypresses that occur while the thread is asleep to not be registered, but if I press something during the timeout it still registers once the timeout is complete. I've tried calling flush(), but this seems to only affect stdout, not stdin:

let term = Term::stdout();

thread::sleep(Duration::from_secs(5));
term.flush()?;

match term.read_key()? {
    _ => ...
}

Thoughts?

Start by reading the Term::read_key and Term::flush entry points used in the example, then inspect how input is handled around the five-second sleep. Determine whether pending keypresses can be discarded before read_key() without affecting stdout; done means keys pressed during the delay are not returned by the subsequent read.